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Table 3 Summary of item-level CFA and IRT evaluations by disease group and all diseases combined and disease-specific versus standardized inter-scale correlationsa

From: Standardizing disease-specific quality of life measures across multiple chronic conditions: development and initial evaluation of the QOL Disease Impact Scale (QDIS®)

Disease Confirmatory Factor Analysis IRT parameters Item r with theta scored Inter-scale correlationse
Χ2 df CFI RMSEA (90 % CI) Factor Loadingsb Residualsc Slopes Thresholds
Arthritis 7037 1127 0.979 0.077 0.91 0.026 2.58 0.99 0.76 0.9996
(0.076–0.079) 0.74–0.94 0.00–0.143 1.18–4.02 −0.83–2.72 0.59–0.86
CKD 1865 1127 0.991 0.058 0.93 0.026 3.55 1.36 0.76 0.9983
(0.053–0.062) 0.76–0.97 0.00–0.202 1.29–5.94 −0.24–2.38 0.62–0.83
Cardiovascular 3658 1127 0.987 0.069 0.92 0.022 3.13 1.18 0.75 0.9998
(0.067–0.072) 0.81–0.96 0.00–0.141 1.62–5.51 −0.20–2.71 0.59–0.86
Diabetes 3991 1127 0.985 0.061 0.91 0.027 2.98 1.85 0.70 0.9992
(0.059–0.063) 0.81–0.97 0.00–0.186 1.36–6.05 −0.29–2.99 0.51–0.81
Respiratory 4847 1127 0.990 0.060 0.92 0.021 3.13 1.50 0.75 0.9999
(0.058–0.061) 0.84–0.97 0.00–0.124 1.64–5.87 0.10–2.67 0.58–0.86
Combined 20,669 1127 0.982 0.074 0.92 0.023 3.05 1.34 0.74 -
(0.073,0.075) 0.81–0.96 0.00–0.158 1.49–5.30 −0.10–2.60 0.58–0.85
  1. Abbreviations: Χ 2 chi-square test of model fit, df degrees of freedom, CFI comparative fit index, RMSEA root mean square error of approximation, CKD chronic kidney disease
  2. aAll entries are median on first line and minimum-maximum on second line unless noted
  3. bLoadings from the completely standardized CFA solution for each disease (rows 1–5) or all diseases combined (row 6)
  4. cAbsolute value of residual correlations after controlling for single factor for each disease (rows 1–5) or all diseases combined (row 6)
  5. dCorrelation between person-level item scores and total bank theta scores for each disease (rows 1–5) or all diseases combined (row 6)
  6. eCorrelation between person-level total bank theta scores estimated using disease-specific and standardized item parameters